(31 July 1009–12 May 1012)
A Roman, son of Peter, a shoemaker of the Ad Pinea district, and his wife Stephania, originally himself named Peter with the nickname Os or Bucca Porci (‘Pig's Snout’), he had been bishop of Albano from 1004 when he succeeded John XVIII. The circumstances of his appointment remain obscure, but like John he owed it to the patrician John II Crescentius, Rome's all-powerful dictator from 1003 to 1012. He altered his name out of respect for the Prince of the Apostles. Reliable information about his activities, apart from the routine granting or confirmation of privileges, is sparse, but it is noteworthy that he was in touch with Henry II of Germany (1002–24), sending envoys to the consecration of the cathedral of his beloved Bamberg (Apr. 1012), ratifying the privileges granted it by John XVIII, and having erected in the Lateran basilica a moment to Silvester II, who had been close to the emperor Otto III. It is probable that he took advantage of this occasion to sound the king on a visit to Rome, but any such project was frustrated not only by the political situation in Germany but by the unyielding opposition of Crescentius. At the request of its bishop (the chronicler Thietmar: 975–1018) he confirmed (1009) the possessions of the recently restored see of Merseburg. There is a tradition that the eastern patriarch Sergius II (1001–19), after the temporary recognition of John XVIII, again struck the pope's name out of the diptychs of Constantinople, but no credence should be given to the suggestion that Sergius IV was himself responsible for this by sending to Constantinople, along with the announcement of his election, a profession of faith containing the Filioque clause. Tensions with the patriarch of Constantinople were, however, increased when he granted a privilege to the archdiocese of Benevento, over which the Byzantines believed they exercised authority. An encyclical in which he purports to appeal to the faithful everywhere to prepare an armed expedition to avenge the destruction of the Holy Sepulchre in Jerusalem by Caliph al-Hakim on 18 Oct. 1009 is spurious; the elements of truth in the story are the undoubted arrival in Rome in Sergius' reign of the news of the disaster, and his attempts (unrelated) to mobilize the Italian powers to drive the Arabs from Sicily.
The disappearance of both Sergius and Crescentius from the scene within less than a week of each other (12 and 18 May), the violent political upheaval which took place in Rome at the time, and the immediate election of a pope of the rival Tusculan family have given rise to the suspicion that neither man may have died a natural death. Sergius was buried in St John Lateran, where his eulogistic epitaph can still be read.
LP ii. 266 f.JW i. 504 f.ZPR 409–24PL 139: 1499–528A. Gieysztor, ‘The Genesis of the Crusades: The Encyclical of Sergius IV’, Medievalia et Humanistica, 5 (1948), 3–34Mann v. 142–54DTC xiv. 1921 f. (É. Amann)J. Gay, Les Papes du XIe siècle et le chrétienté (Paris, 1926)Levillain iii. 1414–15NCE xiii. 15 (J. Sheppard)Seppelt ii. 401 f.